The invention relates to a hot melt processable pressure sensitive adhesive comprising organophilic clay plate-like particles, articles prepared therefrom, and a method of making the pressure sensitive adhesive.
Pressure sensitive adhesives (PSAs) have found use in a variety of applications. PSAs are well known to those of ordinary skill in the art to possess properties including the following: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be removed cleanly from the adherend. Materials that have been found to function well as PSAs are polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear strength. Obtaining the proper balance of properties is not a simple process.
PSAs with performance features are needed that can withstand demanding environments, such as elevated temperatures. The desired performance features can include good peel adhesion, good shear strength, and clean removability.
Additionally, environmental concerns about the use of solvents in the processing of PSAs has led to increased emphasis on solventless processing methods such as hot melt processing. Hot melt processability, however, restricts the polymers that can be used in PSA formulations. For example, crosslinked polymers that have high shear strength are generally not hot melt processable. Accordingly, to otherwise enhance shear strength of a hot-melt processable PSA, some have explored the use of thermoplastic elastomers in such PSA formulations and/or crosslinking the compositions after coating. Nevertheless, these approaches are sometimes limited in the performance characteristics that they are able to achieve.
A need therefore exists for alternative hot melt processable pressure sensitive adhesive (PSA) compositions. A need also exists for hot melt processable PSA compositions that preferably exhibit good high temperature shear strength and good high temperature peel strength, as well as clean removability from an adherend.
In one embodiment, the composition of the invention comprises: (a) at least one elastomer; (b) organophilic clay plate-like particles; and (c) at least one non-volatile organophilic exfoliating agent. The composition is a hot melt processable PSA. In a further embodiment, the organophilic clay plate-like particles are oriented.
The PSA composition of the invention demonstrates good high temperature shear strength in one embodiment. The PSA composition of the invention demonstrates good high temperature peel strength in a further embodiment. The PSA composition of the invention also demonstrates clean removal from an adherend in a further embodiment. Ideally, the PSA composition of the invention also demonstrates good cohesive strength. Good cohesive strength provides a combination of good shear resistance, good peel strength, and clean removability.
The term xe2x80x9cnon-volatile,xe2x80x9d as used herein, refers to those exfoliating agents that generate less than about three weight percent VOC (volatile organic content) when the exfoliating agent is exposed to a temperature of about 110xc2x0 C. xc2x15xc2x0 C. in a forced draft oven for one hour according to ASTM Test Method DS403-93.
The term xe2x80x9corganophilic clay,xe2x80x9d as used herein, refers to a clay that has been surface-modified to convert at least a portion of its surface nature from an organophobic state to an organophilic state (preferably to a hydrophobic state). For example, in one embodiment, a clay may initially have both organophobic and organophilic sites. However, upon modification according to the present invention, at least a portion of the organophobic sites are converted to organophilic sites. In other embodiments, a clay initially contains essentially only organophobic sites and, upon modification according to the present invention, at least a portion of the organophobic sites are converted to organophilic sites. Preferably, at least about 50% of exchangeable cations on the unmodified organophilic clay are exchanged with organophilic modifying cations.
The term xe2x80x9corganophilic exfoliating agent,xe2x80x9d as used herein, refers to an organophilic material capable of separating an organophilic clay sheet into plate-like particles and maintaining the clay in plate-like particles at the use temperature (typically room temperature, i.e., about 21xc2x0 C.).
The term xe2x80x9csolventless,xe2x80x9d as used herein, refers to compositions that are essentially 100 percent solid systems (i.e., systems essentially free of VOC and water). Typically, such compositions have no more than about five weight percent VOC and water, more typically no more than about three weight percent VOC and water. Most typically, such compositions are free of VOC and water.
The term xe2x80x9chot melt processable,xe2x80x9d as used herein, refers to a composition that can transform, for example, by heat and pressure from a solid to a viscous fluid. The composition should be capable of being hot melt processed without being such that the composition chemically transforms, rendering it unusable for the intended application. Typically, hot melt processable compositions are solventless.
The term xe2x80x9coriented,xe2x80x9d as used herein, refers to plate-like particles being positioned in a non-random manner. One skilled in the art would typically be able to observe a composition and determine if the plate-like particles were oriented and, if so, whether or not the plate-like particles were uniaxially or biaxially oriented. In a biaxially oriented system, typically the major surfaces of a majority of the plate-like particles are roughly parallel. This may be the case, for example, for a film that has been stretched in both the x-direction and y-direction. In an uniaxially oriented system, typically a majority of the plate-like particles are aligned via their largest dimension (i.e., their length) roughly in parallel. For example, this would be the y-direction (or xe2x80x9cdown-webxe2x80x9d direction) in the case of a film extruded onto a web and stretched in the y-direction.
The hot melt processable pressure sensitive adhesive (PSA) composition of the present invention comprises at least one elastomer, organophilic clay plate-like particles, at least one non-volatile organophilic exfoliating agent, and optional additives.
An elastomer should be selected that is hot melt processable in order that the composition of the invention be hot melt processable. Hot melt processable elastomers include certain conventional elastomers as well as certain thermoplastic elastomers. These hot melt processable elastomers are typically linear or branched polymers with little or no crosslinking. The composition of the invention typically comprises about 25 to about 98 percent by weight of elastomer based on the total weight of the composition.
Conventional Elastomers
Useful conventional elastomers typically form one phase at about 21xc2x0 C. and have a glass transition temperature of less than about 20xc2x0 C. (more typically less than about 0xc2x0 C.) in addition to exhibiting elastomeric properties. Examples of conventional elastomers that are useful in the present invention include, but are not limited to, natural and synthetic rubbers, polyvinyl ethers, poly(meth)acrylates, polyurethanes, poly-xcex1-olefins, silicones, and combinations thereof.
Natural rubber elastomers useful for formulation as PSAs generally contain masticated natural rubber. Natural rubber may range in grade from a light pale crepe grade to a darker ribbed smoked sheet grade. Representative examples include CV-60 from Goodyear Tire and Rubber Co.; Akron, Ohio, which is a controlled viscosity rubber grade, and SMR-5 from Cargill Inc.; Ontario, N.Y., which is a ribbed smoked sheet rubber grade. Natural rubbers are generally non-tacky and are, therefore, typically formulated with tackifying resins to form PSAs. Other additives, such as antioxidants, are also frequently added to PSA formulations based on natural rubbers.
Useful synthetic rubbers may be either tacky or non-tacky. Synthetic rubber elastomers include, for example, butyl rubber (a copolymer of isobutylene and less than about three weight percent isoprene); polyisobutylene; polyisoprene; polybutadiene; and styrene/butadiene rubber. A specific example of a synthetic rubber is AMERIPOL 101 IA, a styrene/butadiene rubber available from B F Goodrich Co.; Charlotte, N.C.
Polyvinyl ether elastomers are generally employed as blends of homopolymers of different vinyl ethers (e.g., vinyl methyl ether, vinyl ethyl ether, or vinyl isobutyl ether), or blends of homopolymers of vinyl ethers and copolymers (i.e., those polymers derived from at least two chemically different monomers) of vinyl ethers, such as, for example, with (meth)acrylates. Depending upon the degree of polymerization, the homopolymers may be viscous oils, tacky soft resins, or rubber-like substances. Polyvinyl ether elastomers include, for example, those based on vinyl methyl ether, such as LUTANOL M 40, available from BASF Corp.; Mount Olive, N.J., and GANTREZ M 574 and GANTREZ M 555, available from ISP Technologies, Inc.; Wayne N.J.; vinyl ethyl ether, such as LUTANOL A 25, LUTANOL A 50, and LUTANOL A 100, available from BASF Corp.; Mount Olive, N.J.; vinyl isobutyl ether such as LUTANOL 130, LUTANOL 160, LUTANOL IC, LUTANOL I 60D, and LUTANOL I 65D, available from BASF Corp.; Mount Olive, N.J.; and a terpolymer of methacrylate/vinyl isobutyl ether/acrylic acid, such as ACRONAL 550 D, available from BASF Corp.; Mount Olive, N.J.
Poly(meth)acrylate elastomers generally have a glass transition temperature of about xe2x88x9220xc2x0 C. or less. Frequently, these elastomers are copolymers and may comprise, for example, from about 80 to about 100 weight percent of a C3-C12 alkyl ester component such as, for example, isooctyl acrylate, 2-ethyl-hexyl acrylate, and/or n-butyl acrylate, and from about 0 to about 20 weight percent of a polar component, such as, for example, (meth)acrylic acid, ethylene vinyl acetate, N-vinyl pyrrolidone, and/or styrene macromer. The polyacrylate elastomers may be tacky or non-tacky.
The elastomer may comprise a polyurethane elastomer. A representative example of a useful polyurethane elastomer is polyoctadecyl carbamate, which is described in U.S. Pat. No. 2,532,011.
Poly-xcex1-olefin elastomers, also referred to as poly(1-alkene) elastomers, can be any suitable poly-xcex1-olefin, so long as the material has elastomeric properties. Generally such elastomers comprise an uncrosslinked polymer, which may have radiation activatable functional groups grafted thereon as described in U.S. Pat. No. 5,209,971. The poly-xcex1-olefin elastomer may be tacky or non-tacky. If uncrosslinked, the inherent viscosity of the polymer is generally between about 0.7 dL/g and about 5 dL/g as measured according to ASTM D 2857-93, xe2x80x9cStandard Practice for Dilute Solution Viscosity of Polymers.xe2x80x9d In addition, the polymer generally is predominantly amorphous. Useful poly-xcex1-olefin elastomers include, for example, C3-C18 poly(1-alkene) homopolymers and copolymers of propylene with C5-C12 1-alkenes. Preferred poly-xcex1-olefin elastomers include, for example, C5-C12 poly(1-alkene) polymers and copolymers of propylene with C6-C8 1-alkenes.
Silicone elastomers are typically polydimethylsiloxane or polydimethyldiphenylsiloxane polymers that contain residual silanol functionality (SiOH) on the ends of the polymer chain or block copolymers comprising polydiorganosiloxane segments and urea-terminated segments.
Thermoplastic Elastomers
Thermoplastic elastomers exhibit elastomeric properties at room temperature (i.e., about 21xc2x0 C.), but exhibit thermoplastic properties at elevated temperatures at which they can be molded. Representative examples thereof include styrenic block copolymers (such as styrene-diene block copolymers), polyolefins, polyurethanes, polyesters, and combinations thereof.
Styrene-diene block copolymer elastomers are generally of the A-B or [A-B]n type, where A represents a thermoplastic polystyrene block and B represents a rubbery block of polyisoprene, polybutadiene, or one of their hydrogenated versions, such as poly(ethylene/butylene) or poly(ethylene/propylene). Examples of specific styrene-diene block copolymers include, but are not limited to, linear, radial, and tapered styrene-isoprene block copolymers, such as KRATON D 1107, available from Shell Chemical Co.; Houston, Tex. and EUROPRENE SOL TE 9110, available from EniChem Elastomers Americas, Inc.; Houston, Tex.; linear styrene-(ethylene-butylene) block copolymers, such as KRATON G1657, available from Shell Chemical Co.; Houston, Tex.; linear styrene-(ethylene/propylene) block copolymers, such as KRATON G 1750X, available from Shell Chemical Co.; Houston, Tex.; butadiene block copolymers, such as KRATON D 1118, available from Shell Chemical Co.; Houston, Tex., and EUROPRENE SOL TE 6205, available from EniChem Elastomers Americas, Inc.; Houston, Tex.; and radial asymmetric styrene-isoprene block copolymers as described in U.S. Pat. Nos. 5,393,787 and 5,296,547. The polystyrene blocks tend to form domains in the shape of spheroids, cylinders, or lamellae that cause the block copolymer to have two phases.
Polyolefin thermoplastic elastomers are available, for example, from DuPont-Dow Elastomers; Wilmington, Del. under the tradename of ENGAGE. Specific examples thereof include ENGAGE 8150, ENGAGE 8180, ENGAGE 8100, ENGAGE 8452, ENGAGE 8445, ENGAGE 8480, ENGAGE 8490, ENGAGE 8200, and ENGAGE 8840.
Organophilic clay is obtainable by modifying a hydrophilic clay such that the clay is organophilic. Conventional hydrophilic clays are generally not able to be adequately exfoliated according to the present invention. Thus, the present invention utilizes organophilic clays to achieve a higher degree of exfoliation in the clay.
The hydrophilic clay to be modified can be any phyllosilicate or other clay that has a sheet-like structure. Examples thereof include, but are not limited to, hydrated aluminum silicate, kaolinite, atapulgite, illite, halloysite, beidelite, nontronite, hectorite, hectite, bentonite, saponite, and montmorillonite. The smectite clays such as, for example, beidelite, nontronite, hectorite, hectite, bentonite, saponite, and montmorillonite are preferred.
The organophilic clays useful for the invention may be prepared from commercially available hydrophilic clays. The following is an example of a method of preparing organophilic clay:
The hydrophilic clay is stirred and dissolved in water to form an exfoliated hydrophilic clay solution. Then, depending on the clay, exchangeable ions (e.g., sodium or calcium ions), for example, of the hydrophilic clay are exchanged with organophilic modifying cations. Typical organophilic modifying cations comprise onium cations. For example, such cations include, but are not limited to, C2 to C60 alkyl primary, secondary, tertiary, and quaternary ammonium cations and quaternary phosphonium cations. Examples thereof include, but are not limited to, (meth)acrylate ammonium cations, such as 2-(dimethylammonium)ethyl methacrylate cations, octadecylammonium cations, dimethyl dihydrogenated tallow ammonium cations, thiol group functionalized alkyl ammonium cations, and combinations thereof. Exchange of the hydrophilic clay ions with organophlic modifying cations causes the modified clay to precipitate from the water solution. The precipitated clay (which is no longer in an exfoliated state) is then dried to remove excess water.
Some organophilic clays are commercially available. For example, organophilically-modified montmorillonite is available as SCPX CLOISITE 20A, SCPX CLOISITE 15A, SCPX CLOISITE 10A, SCPX CLOISITE 6A, SCPX CLOISITE 30b, and SCPX CLOISITE 2398 from Southern Clay Products; Gonzalez, Tex., and under the trade designation, NANOMER, from Nanocor Inc.; Arlington Heights, Ill.
The composition of the invention typically comprises any suitable amount of organophilic clay. Generally, the amount of organophilic clay present is such that the overall composition is a pressure sensitive adhesive. Preferably the composition includes about 1 to about 40 weight percent of the organophilic clay plate-like particles, more preferably about 1 to about 20 weight percent, and most preferably 1 to about 10 weight percent based on the total weight of the composition. The exact amount varies depending on, for example, the type of elastomer and the presence and amount of other components in the composition.
The composition of the invention typically comprises about 1 to about 75 weight percent of a non-volatile organophilic exfoliating agent based on the total weight of the composition. A non-volatile organophilic exfoliating agent is used to exfoliate the organophilic clay. It has been found that the organophilic clay can be easily exfoliated by exfoliating agents, that are low molecular weight resins. Examples of useful low molecular weight resins include, but are not limited to, tackifying agents and low molecular weight block copolymers such as styrene-isoprene block copolymers, styrene-butadiene block copolymers, and hydrogenated block copolymers. Such exfoliating agents typically have a number average molecular weight of less than about 20,000 g/mol, preferably less than about 10,000 g/mol, and most preferably less than about 5,000 g/mol.
Tackifying agents are the preferred exfoliating agents. However, not all tackifying agents will act as an exfoliating agent in any given system. For a tackifying agent to function as an exfoliating agent according to the present invention, it generally needs to be viscous enough to impart shear forces in the composition upon exfoliation in order to effectively exfoliate the organophilic clay. It is also preferred that such a tackifying agent would minimize or prevent substantial agglomeration of the exfoliated particles. Selecting a tackifying agent in which the organophilic clay is compatible helps to accomplish this preferred embodiment. Suitable tackifying agents can be found in the following groups: aliphatic, aromatic-modified aliphatic, aromatic, and at least partially hydrogenated versions and derivatives thereof.
Examples of tackifying agents that are useful as exfoliating agents include, but are not limited to, rosins, such as wood rosins and their hydrogenated derivatives; derivatives of rosins, such as FORAL 85, a stabilized rosin ester from Hercules Chemical Co.; Wilmington, Del., the SNOWTACK series of gum rosins from Tenneco Corp.; Greenwich, Conn., and the AQUATAC series of tall oil rosins from Arizona Chemical Co.; Panama City, Fla.; terpene resins of various softening points, such as xcex1-pinene and xcex2-pinene, available as PICCOLYTE A-115 and ZONAREZ B-100 from Arizona Chemical Co.; Panama City, Fla.; petroleum-based resins, such as the ESCOREZ 1300 series of aliphatic olefin-derived resins and the ESCOREZ 2000 series of aromatic/aliphatic olefin-derived resins from Exxon Chemical Co.; Houston, Tex.; and synthetic hydrocarbon resins, such as the PICCOLYTE A series of aromatic resins such as PICCOTEX LC-55WK; and aliphatic resins, such as PICCOTAC 95, available from Hercules Chemical Co.; Wilmington, Del.
Particularly preferred are resins derived by polymerization of C5 to C9 unsaturated hydrocarbon monomers, polyterpenes, synthetic polyterpenes and the like. Examples of such commercially available resins of this type are WINGTACK PLUS tackifying agents, available from Goodyear Tire and Rubber Co.; Akron, Ohio; REGALREZ 1126 tackifying agents, available from Hercules Chemical Co.; Wilmington, Del.; and ESCOREZ 180, ESCOREZ 1310, and ESCOREZ 2393 tackifying agents, all available from Exxon Chemical Co.; Houston, Tex.
Additives may optionally be included in the PSA composition of the invention. The type and amount of additives depend on, for example, the nature of the elastomer, clay plate-like particles, and exfoliating agent. Examples of additives include, but are not limited to, general tackifying agents, plasticizers, antioxidants, pigments, curing agents, adhesion promoting agents, and combinations thereof.
Tackifying Agents
In some cases, the non-volatile organophilic exfoliating agent may serve to tackify the elastomer. The composition of the invention typically comprises about 0 to about 75 weight percent, preferably about 0 to about 60 weight percent, and most preferably about 0 to about 50 weight percent of a tackifying agent based on total weight of the composition. The aforementioned weight percentages with respect to tackifying agents include those tackifying agents that are also exfoliating agents in addition to those that are not.
Adhesion Promoting Agents
An adhesion promoting agent may optionally be included in the composition of the invention. Adhesion promoting agents are materials that improve the bonding of the PSA to a substrate. Examples of useful adhesion promoting agents include, but are not limited to, those selected from trimethylolpropane (TMPTA), hexanediol diacrylate (HDDA), and pentaerythritol acrylate (PETA).
Preferably, the composition comprises about 0 to about 10 weight percent of an adhesion promoting agent (more typically about 0.1 to about 10 weight percent, if included) based on the total weight of the composition, preferably about 0 to about 5 weight percent, and most preferably about 0 to about 2 weight percent.
Mixing can typically be done by any method that results in a substantially homogeneous distribution of the components. The composition of the invention is typically prepared by melt mixing the components in a molten or softened state using devices that provide dispersive mixing, distributive mixing, or a combination thereof. Both batch and continuous methods of mixing may be used. Examples of batch methods include internal mixing and roll milling. Examples of continuous methods include single screw extruding, twin screw extruding, disk extruding, reciprocating single screw extruding, and pin barrel single screw extruding. Continuous methods can utilize distributive elements, pin mixing elements, static mixing elements, and dispersive elements such as MADDOCK mixing elements and SAXTON mixing elements.
It is difficult to exfoliate organophilic clay by hot melt mixing clay with elastomer only. It has been found that hot melt processing of the organophilic clay directly with an elastomer leads to limited exfoliation of the organophilic clay, leaving many clay aggregates or sheets. Therefore, an exfoliating agent is utilized according to the present invention.
Several different sequences may be used to mix the elastomer, organophilic clay, exfoliating agent, and optional additives when preparing the hot melt processable PSA composition of the invention. The elastomer, organophilic clay, exfoliating agent, and optional additives can, for example, be simply mixed while heating under shear forces, such as in an extruder or a mixer such as a BRABENDER mixer (commercially available from C. W. Brabender Co.; South Hackensack, N.J.) or a BANBURY mixer. If the composition is prepared in a mixer, rather than an extruder, it can subsequently be transferred to an extruder. Alternatively, a master batch of pre-exfoliated organophilic clay can be prepared by mixing the organophilic clay and exfoliating agent while heating under shear conditions. This master batch can then be mixed with the elastomer to form the hot melt processable PSA composition.
A master batch of pre-exfoliated organophilic clay can be prepared, for example, by compounding the organophilic clay and exfoliating agent in a twin screw extruder such as a 33 millimeter co-rotating twin screw extruder commercially available from APV Chemical Machinery Inc.; affiliated with Davis-Standard, a Crompton Company; Pawcatuck, Conn. or a BRABENDER mixer (commercially available from C. W. Brabender Co.; South Hackensack, N.J.). The compounding temperature is typically from about 100xc2x0 C. to about 180xc2x0 C. depending on the melt processing temperature of the exfoliating agent. The compounding temperature should be selected such that it is above the softening point of the exfoliating agent but below the decomposition temperature of the components.
After pre-compounding organophilic clay with the exfoliating agent to produce a master batch, the master batch can be hot melt mixed with the elastomer to produce a hot melt processable PSA composition. Because the final exfoliation of the organophilic clay is much more complete when the organophilic clay is pre-exfoliated prior to mixing with the elastomer, this method may be preferred over the direct mixing of elastomer, organophilic clay, and exfoliating agent.
After the mixing step, whether done in an extruder or a mixer, the composition can be formed into a coating by continuous hot melt forming methods. Continuous forming methods include, for example, drawing the PSA composition out of a film die and subsequently contacting the composition to a moving plastic web or other suitable substrate. A related continuous forming method involves extruding the composition and a co-extruded backing material from a film die and subsequently cooling the construction to form a PSA tape. Other continuous forming methods involve directly contacting the molten composition to a rapidly moving plastic web or other suitable substrate. In this method, the composition can be applied to the moving web using a die having flexible die lips, such as a reverse orifice coating die and/or other contact dies using rotating rods. After forming, the PSA coatings can be solidified by quenching using direct methods, such as chill rolls or water baths, and indirect methods, such as air or gas impingement.
PSA articles of the invention can be made, for example, by applying the composition of the invention to a substrate by various hot melt coating processes. Any suitable substrate can be used.
A particularly preferred article is a tape. Examples of suitable tapes include, but are not limited to, cloth-backed tapes, paper-backed tapes, film-backed tapes, and transfer tapes. A PSA tape can be prepared by coating a layer of PSA on a backing. The exposed surface of the PSA coating may subsequently be applied to a surface from which it could be released later or directly to the surface to which it is intended to adhere.
A transfer PSA tape can be made by coating the PSA composition between two liners, both of which are coated with a release coating. The release liners often comprise a clear polymeric material such as polyolefin or polyester that is transparent to ultraviolet radiation.
The degree of organophilic clay exfoliation was found to affect adhesive properties of the composition. The exact degree of exfoliation needed, however, depends upon the particular application of compositions of the invention. Preferably, the organophilic clay is effectively exfoliated to a degree such that, when used as the adhesive in a tape according to the present invention, the tape has a 70xc2x0 C. shear strength that is at least about 50 percent higher, more preferably at least about 100 percent higher, even more preferably at least about 200 percent higher, and most preferably at least about 300 percent higher, than that of a control tape that is otherwise identical except for the control tape being free of organophilic clay, when measured according to ASTM Test Method D3654-88.
Similarly, it is preferred that the organophilic clay is effectively exfoliated to a degree such that, when used as the adhesive in a tape according to the present invention, the tape has a 180xc2x0 peel adhesion at 75xc2x0 C. that is at least about 50 percent higher, more preferably at least about 100 percent higher, and most preferably at least about 200 percent higher than that of a control tape that is otherwise identical except for the control tape being free of organophilic clay. Preferably, the tape of the invention has a 180xc2x0 peel adhesion at 100xc2x0 C. that is at least about 50 percent higher, more preferably at least about 100 percent higher, and most preferably at least about 200 percent higher than that of a control tape that is otherwise identical except for the control tape being free of organophilic clay. Preferably, the tape of the invention has a 180xc2x0 peel adhesion at 125xc2x0 C. that is at least about 50 percent higher, more preferably at least about 100 percent higher, and most preferably at least about 200 percent higher than that of a control tape that is otherwise identical except for the control tape being free of organophilic clay.
The coated composition may optionally be cured by exposure to, for example, thermal (i.e., heat) or other radiation. If heat is used to cure the composition, a thermal curing agent is preferably included in the composition, preferably one that activates at a temperature above the hot melt processing temperature of the composition. Curing by exposure to ultraviolet radiation is generally preferred. Suitable radiation sources include actinic (such as ultraviolet, for example), electron beam (e-beam), and similar sources. A photocuring agent is generally added to the composition when actinic radiation is employed. Photocuring agents should be selected such that they are compatible with the composition of the invention.